Nucleic Acid Delivery Excipients: Pioneering the Future of Genetic Medicine

Nucleic acid-based therapeutics, such as DNA and RNA-based drugs, offer unparalleled potential in treating a myriad of genetic disorders, cancers, and infectious diseases. However, the successful delivery of these delicate biomolecules to the target site remains a significant challenge. This is where excipients play a crucial role in enhancing the efficacy and safety of nucleic acid delivery.

Understanding Nucleic Acid Delivery Excipients

Nucleic acid delivery excipients are essential for the safe and efficient delivery of nucleic acids (such as DNA, RNA, and oligonucleotides) to target cells. Their primary functions include:

• Protection: Shielding nucleic acids from degradation by nucleases in the extracellular environment.
• Stability: Enhancing the chemical stability of nucleic acids during storage and transport.
• Targeted Delivery: Facilitating the targeted delivery of nucleic acids to specific tissues or cells.
• Cellular Uptake: Improving the uptake of nucleic acids by cells and ensuring their release into the intracellular environment.

Types of Nucleic Acid Delivery Excipients

Lipid-Based Excipients

Cationic Lipids: These positively charged lipids form complexes with negatively charged nucleic acids, aiding in cellular uptake through endocytosis. Examples include DOTMA, DOTAP, and DC-Chol.

Ionizable Lipids: These lipids become positively charged at acidic pH, facilitating endosomal escape. A prime example is DLin-MC3-DMA, used in FDA-approved siRNA therapies.

PEGylated Lipids: These lipids are modified with polyethylene glycol (PEG) to enhance circulation time and reduce immune recognition. PEGylated lipids are integral to the formulation of lipid nanoparticles (LNPs).

Polymer-Based Excipients

Polyethyleneimine (PEI): A highly effective polymer for gene delivery, PEI forms stable complexes with nucleic acids and promotes endosomal escape through its "proton sponge" effect.

Polylactic-co-glycolic acid (PLGA): Biodegradable and biocompatible, PLGA is used to encapsulate nucleic acids in nanoparticles, providing controlled release.

Chitosan: A natural polymer derived from chitin, chitosan offers biocompatibility and can be chemically modified to enhance its delivery properties.

Peptide-Based Excipients

Cell-Penetrating Peptides (CPPs): Short peptides that facilitate the translocation of nucleic acids across cellular membranes. TAT peptide and penetratin are notable examples.

Endosomal Escape Peptides: These peptides aid in the release of nucleic acids from endosomes into the cytoplasm, improving delivery efficiency.

Fig.1 (a) Tricyclic cell-penetrating peptides for efficient delivery of functional antibodies into cancer cells^[1], (b) Endosomal escape cell-penetrating peptides significantly enhance pharmacological effectiveness and CNS activity of systemically administered antisense oligonucleotides^[2].

Mechanisms of Action

The efficacy of nucleic acid delivery excipients hinges on their ability to navigate several biological barriers. Key mechanisms include:

• Complexation: Excipients form complexes with nucleic acids, enhancing their stability and preventing degradation.
• Cellular Uptake: Through endocytosis or direct membrane penetration, excipient-nucleic acid complexes enter target cells.
• Endosomal Escape: Excipients facilitate the release of nucleic acids from endosomes into the cytoplasm, where they can exert their therapeutic effect.
• Targeting: By incorporating ligands or antibodies, excipients can be directed to specific cell types, enhancing the precision of delivery.

Emerging Trends and Innovations

The field of nucleic acid delivery excipients is rapidly evolving, driven by the need for more efficient and safer delivery systems. Emerging trends include:

Hybrid Nanoparticles

Combining different types of excipients (e.g., lipid-polymer hybrids) to leverage the advantages of each.

Fig.2 Lipid-polymer hybrid nanoparticles (LPNs) are core-shell nanoparticle structures comprising polymer cores and lipid/lipid-PEG shells^[2].

Biodegradable Excipients

Development of excipients that degrade into non-toxic byproducts, minimizing long-term side effects.

Responsive Excipients

Excipients designed to respond to specific stimuli (e.g., pH, enzymes) for controlled release of nucleic acids.

Fig.3 (a) Building blocks of biodegradable cationic and ionizable cationic lipids^[4], (b) Impact of pH on the protonation and structure of charge-reversible lipid-based nanoparticles encapsulating siRNA^[5].

Personalized Delivery Systems

Tailoring excipients to individual patient needs based on genetic and molecular profiles. Personalized drug delivery systems (PDDS), implying the patient-tailored dose, dosage form, frequency of administration and drug release kinetics, and digital health platforms for diagnosis and treatment monitoring, patient adherence, and traceability of drug products, are emerging scientific areas.

Fig.4 A concept of an interactive personalized treatment connecting patients, physicians and PDDS via "digital health" systems and manufacturing PDDS on-demand via "mass customization"^[6].

Conclusion

Nucleic acid delivery excipients are at the forefront of genetic medicine, playing a critical role in the success of nucleic acid therapies. By enhancing the stability, delivery, and efficacy of these therapies, excipients are paving the way for new treatments that can address previously untreatable conditions. As research and innovation continue to advance, the future of nucleic acid delivery promises even greater breakthroughs, bringing us closer to the full potential of genetic medicine.

References

1. Tietz O, et al. Nature Chemistry, 2022, 14, 284-293.
2. Dastpeyman M, et al. International Journal of Pharmaceutics, 2021, 599, 120398.
3. Hadinoto K, et al. European Journal of Pharmaceutics and Biopharmaceutics, 2013, 85(3), 427-443.
4. Thai Thanh Hoang Thi, et al. Vaccines, 2021, 9(4), 359.
5. Jörgensen AM, et al. Small, 2023, 19(17), 2206968.
6. Raijada D, et al. Advanced Drug Delivery Reviews, 2021, 176, 113857.

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